The Failure of the Thermodynamics of Computation(2010)

Summary

When a Good Theory meets a Bad Idealization: The Failure of the Thermodynamics of Computation John D. Norton Center for Philosophy of Science Department of History and Philosophy of Science University of Pittsburgh http://www.pitt.edu/~jdnorton Revised and improved edition, July 2013. For historians here is an archived copy of the old version from 2010. Experts who want to see the no go result described in 650 words, should go to "No Go Result for the Thermodynamics of Computation" The thermodynamics of computation seeks to identify the principled thermodynamic limits to computation. It imagines computations carried out on systems so small that their components are of molecular sizes. The founding tenet of the analysis is that all the processes excepting one can in principle be carried out in a non-dissipative manner, that is, in a manner in which no thermodynamic entropy is created or passed to the surroundings. The sole class of necessarily dissipative processes is identified by the central dogma as those physical processes that implement a logical, many-to-one mapping. The universal example of such a process is erasure. It takes a memory device that may be in many different states and maps it to one, a single reset state. Elsewhere I have argued that the thermodynamics of computation is gravely troubled. Its leading principle, Landauer's Principle, connects erasure to entropy dissipation. Yet there is still no sound justification for it. The proofs that have been given rest on fallacies or misapplications of statistical and thermal physics. The purpose of this site is to describe a different problem in the theory that I hope will be of more general interest in philosophy of science. It gives a concrete example of what can go wrong if one uses idealizations improperly. An ineliminable assumption of the thermodynamics of computation is that one can employ a repertoire of non-dissipative processes at molecular scales. These processes are thermodynamically reversible...